Abstract
This study investigates the mesoscale deagglomeration mechanisms of multi-walled carbon nanotubes (MWCNTs) in aqueous solutions with and without added surfactant (Triton X-100), using high-speed imaging and numerical simulations. High-speed observations revealed that within the cavitation zone (CZ, defined as the region of high bubble intensity), the addition of surfactant had no obvious effects on deagglomeration behaviour, with most agglomerates remaining intact and only occasional fragmentation events observed. In contrast, in regions outside the CZ, surfactant addition significantly increased the number and stability of microbubble clusters, leading to more frequent interactions with MWCNT agglomerates. Numerical simulations performed under matched experimental conditions confirmed a spatial variation in bubble dynamics, with enhanced microbubble formation and persistence in surfactant-containing solutions, particularly at distances away from the sonotrode. These findings provide direct mechanistic evidence that surfactant not only stabilises dispersed CNTs but also facilitates microbubble-mediated deagglomeration outside the CZ. The results highlight the role of structured bubble activity in extending the effective dispersion region during ultrasonication, offering insight into the optimisation of CNT processing in surfactant-assisted systems.